In the fast-food industry, pre-cooked food is typically packaged in flexible material (e.g., plastic bags or film) and then frozen or refrigerated to be preserved until needed. To be prepared for consumption, the food must be heated or “rethermalized.” The food may then be held at a proper temperature until it is finally served.
Various techniques are used to rethermalize the food before it is served, such as by water bath, steam, convection with steam, forced convection, natural convection, infrared, conduction, and microwave. However, each of these techniques has certain drawbacks. In a water bath, for example, packages of frozen or refrigerated food are placed in a reservoir of heated water. This operation requires water supply lines, drain lines, input of substantial energy to heat the water and maintain it at a high temperature, venting of steam and water vapor from the reservoir, and regular cleaning of the reservoir. If a bag containing pre-cooked food breaks or leaks in the water bath, the water becomes contaminated and requires personnel to drain, refill, and reheat the water bath.
Two general disadvantages of existing rethermalization techniques are the inability to impart unique thermal treatment to separate bags of food, and the inability to accomplish even or uniform thermal treatment throughout the thickness of the food. In techniques such as water bath, steam, and various forms of convection, food bags are treated in a common chamber. Because the bags are not treated in individual compartments, they cannot be heated to different temperatures or at different rates. Rethermalization techniques such as infrared and microwave do not uniformly rethermalize food because infrared penetration depths vary significantly for various foods, and microwaves are not absorbed well by frozen food.
Another disadvantage of some existing rethermalization techniques, such as infrared, is that the pre-cooked food must be removed from its packaging and placed in a separate container before being re-heated. This process is inefficient and can reduce the amount of time the food can be held in a high-quality state prior to serving.
There is a need, therefore, for an improved process for rethermalizing food.